lighting: move computation of color channels count to new function

We might be using this in more places.

src/gc_gl.c

@@ -2060,6 +2060,19 @@ static LightMasks prepare_lighting()
     return masks;
 }
 
+static int count_color_channels()
+{
+    int color_provide = 0;
+    if (glparamstate.cs.color_enabled &&
+        (!glparamstate.lighting.enabled || glparamstate.lighting.color_material_enabled)) { // Vertex colouring
+        if (glparamstate.lighting.enabled)
+            color_provide = 2; // Lighting requires two color channels
+        else
+            color_provide = 1;
+    }
+    return color_provide;
+}
+
 void _ogx_update_vertex_array_readers()
 {
     if (glparamstate.cs.vertex_enabled) {
@@ -2538,14 +2551,7 @@ static bool setup_draw(const OgxDrawData *draw_data)
 
     if (!glparamstate.current_program) {
         uint8_t texen = glparamstate.texture_enabled;
-        uint8_t color_provide = 0;
-        if (glparamstate.cs.color_enabled &&
-            (!glparamstate.lighting.enabled || glparamstate.lighting.color_material_enabled)) { // Vertex colouring
-            if (glparamstate.lighting.enabled)
-                color_provide = 2; // Lighting requires two color channels
-            else
-                color_provide = 1;
-        }
+        uint8_t color_provide = count_color_channels();
         _ogx_arrays_setup_draw(draw_data,
                                glparamstate.cs.normal_enabled, color_provide, texen);